On 03/03/22 at 11:27am, Eric DeVolder wrote:
> For kexec_file_load support, the loading of the crash kernel occurs
> entirely within the kernel, and as such the elfcorehdr is readily
> identified (so that it can be modified upon hotplug events).
>
> This change enables support for kexec_load by identifying the
> elfcorehdr segment in the arch_crash_hotplug_handler(), if it has
> not already been identified.
>
> In general, support for kexec_load requires corresponding changes
> to the userspace kexec-tools utility. It is the responsibility of
> the userspace kexec utility to ensure that:
> - the elfcorehdr segment is sufficiently large enough to accommodate
> hotplug changes, ala CRASH_HOTPLUG_ELFCOREHDR_SZ.
> - provides a purgatory that excludes the elfcorehdr from its list of
> run-time segments to check.
> These changes to the userspace kexec utility are available, but not
> yet accepted upstream.
These backgroud information should be put in cover letter, or in patch
where they won't be grabbed into the final commit log.
>
> Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
> ---
Here, if you want to put some status or backgroud information and expect
they are not got into log, this is a appropriate place.
> arch/x86/kernel/crash.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 5da30e2bc780..45cc6e3af63e 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -486,6 +486,32 @@ void arch_crash_hotplug_handler(struct kimage *image,
> void *elfbuf = NULL;
> unsigned long mem, memsz;
>
> + /*
> + * When the struct kimage is alloced, it is wiped to zero, so
> + * the elf_index_valid defaults to false. It is set on the
> + * kexec_file_load path, or here for kexec_load.
I would make the last line as:
kexec_file_load path, or here for kexec_load if not already
identified..
> + */
> + if (!image->elf_index_valid) {
> + unsigned int n;
> +
> + for (n = 0; n < image->nr_segments; n++) {
> + mem = image->segment[n].mem;
> + memsz = image->segment[n].memsz;
> + ptr = map_crash_pages(mem, memsz);
> + if (ptr) {
> + /* The segment containing elfcorehdr */
> + if ((ptr[0] == 0x7F) &&
> + (ptr[1] == 'E') &&
> + (ptr[2] == 'L') &&
> + (ptr[3] == 'F')) {
Can it be like memcmp(ptr, ELFMAG, SELFMAG) as we have done in
parse_crash_elf_headers()? With that, one line is taken.
> + image->elf_index = (int)n;
> + image->elf_index_valid = true;
> + }
> + }
> + unmap_crash_pages((void **)&ptr);
> + }
> + }
> +
> /* Must have valid elfcorehdr index */
> if (!image->elf_index_valid) {
> pr_err("crash hp: unable to locate elfcorehdr segment");
> --
> 2.27.0
>
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